Fluid heater



July 5, 1955 L. J. MCCARTHY 2,712,303

FLUID HEATER Original Filed April 2a, 1948 s Sheets-Sheet 1 lNVENTOR MyM ATTO R N EY July 5, 1955 L. .1. MCCARTHY 2,712,3 3

FLUID HEATER Original Filed April 23, 1948 5 Sheets-Sheet 2 INVENTOR 4 .11. Mcawn/r,

ATTO R N EY ka/KM July 5, 1955 1.. J. MCCARTHY FLUID HEATER 5 Sheets-Sheet 3 Original Filed April 23, 1948 INVENTOR A AW/Pz-A/ c":- Mb (I l/Pr);

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ATTORNEY July 5, 1955 J. MCCARTHY 2,712,303

FLUID HEATER Original Filed April 23, 1948 5 Sheets-Sheet 4 INVENTOR L 4W/Pf/V6T' c/. M: 641F777);

ATTO RN EY y 1955 J. M CARTHY 2,712,303

FLUID HEATER Original Filed April 23, 1948 5 Sheets-Sheet 5 INVENTOR .4 flWif/VCZ' a. Me 674F777) ATTO R N EY United States Patent FLUID HEATER Lawrence J. McCarthy, Englewood, N. 1., assignor to Chemical Construction Corporation, New York, N. Y., a corporation of Delaware Original application April 23, 1948, Serial No. 22,782. Divided and this application May 11, 1951, Serial No. 225,793

8 Claims. (Cl. 122-319) This invention relates to an improved apparatus for the application. of heat to fluids. It is particularly adapted to conducting endothermic reactions, such as gas reforming. This application is a division of application, Serial No. 22,782, filed April 23; 1948, now Patent 2,660,519.

In Patent 2,211,903, issued to me on August 20, 1940, there is described a heater for fluids having a radiant heating chamber with fluid conducting tubes extending vertically through the chamber. These tubes are arranged in a plurality of banks radiating substantially from the central portion of the chamber so as to divide it into a plurality of heating cells so that at least one cell is disposed on each side of each bank of tubes. The tubes in each bank are connected in series and with the tubes of one or more banks so that the fluid to be heated flows successively through a plurality of banks in the single heating chamber. Radiant heat is supplied to the tubes by heating the Walls the wall and also by wall burners.

The present invention relates to new and useful improvements in the furnace described in my patent referred to above. My improved furnace is intended to be a heater for fluids generally and is particularly useful for conducting endothermic reactions. For convenience, it will be described in connection with the production of hydrogen by the catalytic reaction of methane with steam, although the invention is not limited thereto.

One of the objects of my invention is to improve the heater or furnace described in my patent referred to above. Another object is to provide a furnace in which the hot gases of combustion will flow substantially longitudinally and parallel to the reaction tubes for that portion of their length exposed to radiant heat. Another object is to equalize the draft in the various cells formed by the plurality of radial banks of tubes disposed in a combustion chamber. A further object is to provide an overhead suspension arrangement for the reaction tubes in which the tubes will be free to expand downwardly into the furnace from the point of their suspension. Another object is to supply preheated air to burners located in the floor of the furnace and adjacent the tubes by a manifold in each cell which is an integral part of the floor thereof.

With the above and other objects in view the invention, therefore, consists in the various arrangements andcombinations of apparatus elements hereinafter to be specifically described with particular reference to the preferred. embodiments thereof illustrated in the accompanying drawings. In the drawings:

Figure 1 is a vertical section taken along the line 1*1 and in the direction of the arrows of Figure 2;

Figure 2 is a section taken along the line 2-2 and in the direction of the arrows of Figure 1;

Figure 3 is a section partly broken away along the line 3-3 and in the direction of the arrows of Figure 1;

Figure 4 is a view in perspective of the gas collecting chamber showingthe manifold arrangement;

Figure 5 is a section taken along the line 5'-- 5 and in the direction of the arrows of Figure 1;

Figure 6 is a section taken along the line 6 -6 and in the direction of the arrows of Figure 5;

Figure 7 is a section in detail showing the suspension of a tube. 7

Referring to the drawings, in Figure l a furnace assembly shows a combination in which a foundation 1 made of a suitable structure of iron I-bearns supports cylindrical load-bearing walls 2 which enclose aradiant heating section 3, a gas collecting section 4 and a space 5 in which are located the suspension means and inlet and outlet manifolds. Banks of vertical heating tubes or catalytic tubes 6, preferably in cruciform arrangement, extend downwardly through both the gas-collecting chamber 4 and the radiant heating chamber 3 and divide both chambers into four heating cells, the tubes being free to expand into the wells 7 placed in the floor of the furnace.

Transverse trusses or beams 9 mounted at the top of the load-bearing walls 2 and supported by them extend across the central portion of the furnace. Preferably two transverse trussesor beams 9 are used and attached 'to them at one end and to the load-bearing walls 2 at the other are support angles 8 which, together with beam 9, frame the top of the furnace. On this structure cover plates 8a rest. Suspended from the beams 9 are the tension members 10 which extend downwardly into the central portion of the furnace. -An upper set of transverse beams 11 and a lower set 12 are attached at their inner ends to the suspension members 10 and at their outer ends to the load-bearing walls 2. The tension members 10 and the sets of transverse beams 11 and 12 cooperate with the load-bearing walls 2 to outline the general contours of with burners disposed in the bottom of each cell adjacent 5: the gas-collecting chamber which in turn takes the outline of the tube bank arrangement.

The walls 13 and the ceiling 14 of the radiant heating section 3 and the walls 15 and top 16 of the gas-collecting chamber 4- are composed of suitable refractory material which protects the load-bearing walls 2 and the suspension means including members 8, 9,10, 11 and 12 from the hot products of combustion. To cool the suspension means, ventilating ports 17 are provided in the space 5 to permit circulation of air therein. The bustle pipe" 18 .21.; Surrounds the furnace and supplies preheated air to a manifold under each cell which forms an integral part of the floor for the cell. The air flows from the manifold into the banks of burners which are placed in each cell adjacent the ends of the vertical tubes.

The flow of the fluid reactants through the furnace can best be illustrated by referring to Figure 4, which shows a perspective arrangement of the gas headers or manifolds which are located in the space 5. The mixture of relatively cool methane and steam is led into the inlet manifolds 19 provided for the tubes of each cell and passes through pipes 20 into the catalytic reaction tubes 6. In the catalytic reaction tubes, which are the nested tube type, the fluids pass downwardly between the outer and inner tube and in contact with the catalyst, where the t'= reaction takes places, and then pass up through the inner tube and into the pipes 21 which lead them to the outlet manifolds 22 from which the fluids are withdrawn from the furnace. Instead of passing the fluids counterc'up rently to the hot products" of combustion as shown, they may be passed concurrently with the hot gases by introducing' the fluids into the tubes through manifolds 22 and withdrawing them from manifolds 19. v

The flow of the heating gases during the furnace operation is best shown by referring-to Figures 1, 4, 5 and 6.

-' Preheated air enters the furnace from bustle 18 passing into the manifold which forms a part of the floor in each cell and passes up alongside the burners embedded therein and which are adjacent the tubes. In each cell the hot products of combustion pass from the burners substantially parallel. to the portion of the tubes in the radiant heating chamber and collect in the sections 23, 24, 2S and 26 which constitute the gas-collecting chamber 4. In chamber 4 the gases pass transversely to the tubes, leaving the chamber through section 26 which connects with a stack.

Upper access doors 27 and lower access or explosion doors (not shown) are placed in the walls 2. Access to the space 5 may also be had through the top of the. furnace by removing plates 8a. The doors 27 may also cooperate with the ports 17 to circulate cooling air to this space. 7

Since the heat for the reactions is supplied principally by radiant heat and since the reaction in each of the tubes should proceed equally, it is desirable that the hot gases pass substantially parallel and longitudinally of the portion of the tubes in the radiant heating chamber. When the gases pass through the radiant chamber in this manner, they radiate heat to the tubes andto the walls of the chamber which in turn re-radiate heat to the tubes so that all of the tubes are heated alike. The flow of the hot gases longitudinally of the tube in the radiant heating zone is accomplished by having the burners in the bottom, of the furnace and adjacent the tubes and by placing the gas-collecting chamber above the radiant heating chamber, and also by varying the area of the openings between the two chambers in such a way that the draft in each of the sections 23, 24, 25 and 26 of the collecting chamber is substantially equal.

The arrangement to equalize the draft is illustrated in Figures 1 and 2. In those figures, the Walls 15 of the gas-collecting chamber are shown, while below these walls and at the entrance from the radiant heating chamber 3 to the gas-collecting chamber 4 are the baffles 28. These baffies which may be extensible, are a continuation of the roof 14 of the radiant heating chamben. They extend beyond the walls 15 for varying distances in such a way as to equalize substantially the draft within each cell as well as in one cell with respect to another. Thus in each section 23, 24 and 25 of the gas-collecting chamber 4, the cross sectional area of the opening into the section is reduced progressively from the walls 2 to the center of the furnace substantially as shown in Figure 2. section 26, however, which contains the outlet 29 to the stack, the cross sectional .area of the opening decreases progressively from the center of the furnace to the walls 2. With this draft equalizing arrangement and by locating the burners adjacent the tubes, thereis substantially no tendency for the gases to deviate from their'pathlongitudinally of the tubes in the radiant heating chamber or for the gases to pass therein from one cell to another in the direction of the flue outlet. These features are among the principal advantages ofmy invention.

I will now describe the manner in which the tubes are'suspended. In Figure l the I-beams 30 which are located at suitable intervals external to the gas-collecting chamber 4 are fastened at their lower ends to the transverse beams 12. They are attached at their upper ends to channel beams 11 by means of clips 32. The channels 11 are attached at their inner ends to the tension members by means of clips 31 and on the channels 11 rest tube support plates 33.

The manner in which the plates rest on the channels is shown more fully in Figure 3. This figure shows the general relationship between the I-beams 30, the clips 32, the channels 11 and the tube support plates 33. Also shown are the tension members 10 and clips 31. There is an individual support plate 33 for eachof the tubes and each plate is provided with a hole 34 in its center through which the tube is inserted. The four tubes around the center of the furnace are supported by the four triangular type plates 35 which, as shown, rest on channels 11. These four plates are also supported by diagonal tie members (not shown) which are framed beneath the plates 35 and are attached to tension members 10.

.The suspension of the tubes is shown in more detail and tube 6.

The manner in which the suspension means supports the weight of the insulation, which forms a part of the ceiling of the radiant heating chamber and the walls and top of the gas-collecting chamber as well as the baffle between the two chambers, is shown by Figures 1 and 2.

It will be seen that the ceiling 14 of the radiant heating chamber and the walls 15 of the gas-collecting chamber are supported by the transverse beams 12 which comprise two angles fastened together as illustrated by the numeral 12a in the Figure l. The individual pieces of refractory in the walls 15 may also be attached to prong-like projections attached to angles which may be attached to,

i-beams 3t} and spaced above and parallel to 12a. Rods 38 are'supporterl at one end by the load-bearing walls 2- i and at the other end on the angles 12a. From this system of rods which is shown in Figure 2 the individual pieces of refractory in the ceiling 14 are hung by means of hooks The top of the gas-collecting 39 shown in Figure l. chamber 16 is hung in a like manner from the channels not shown.

The weight of the baffie 28 which is an extension of the ceiling 14 is also borne by the transverse beam 12. Since the draft in the gas-collecting chamber is equalized by extending the baffic for various distances into the opening between the gas-collecting chamber 4 and the radiant heating chamber 3, some of the pieces of refractory material which form the baffle will extend farther into the opening and may require additional support. Such pieces; of refractory as well as the smallest ones may be supported by a'ttaching a plate or plates or prong-like plates to the bottom of the transverse member 12. By providing a hole or a slot in the piece of refractory into which the plate attached to the transverse member is insertable, thej refractory will be supported. It should be noted that the plates referred to above may be extensible plates.

. The burner arrangement and the means for supplying This. figure shows the bustle pipe 18 which surrounds the lower, portion of the furnace and which is attached to it by the. clips 41. The ducts 42 lead, the preheated air from the bustle 18 into the manifolds which constitute an integral.v part of the floor vof each cell of the furnace. In the pre-. ferred form of the furnace there are twenty tubes in cruci-. form arrangement and for each cell formed by the tubes:

preheated air to the burners is shown in Figure 5.

there, are five burners placed in the manifold of each cell This figure also shows the clips 41, bustle 18. the duct 42,

provided with the damper 43, the manifold 44 and burner 40. The flow of the preheated air is shown generally by the arrows, the air flowing from the bustle through the duct and. into the manifolds. From the manifold the air passes through the opening 45 in the bottom of the burner: and. then passes up through the burner where it contacts the fuel issuing from the burner nozzles.

.The top of the manifold is formed by the plate 46 which is attached to the load-bearing wall 2. On this top platerests the insulation 13. The top plate 46 rests onthe channels 47 which form the sides of the manifold and which are also a part of the iron construction 1, shown in Figure l, which is the loadrbearing foundation referred to This is done by attaching angles to the lower edge of the channels 11 which support the rods to which the hooks, which are fastened to the individual pieces of refractory, are attached. For clarity in the drawing, the angles, rods and hooks attached to the channels 11 are 5 earlier. The bottom of the manifold is formed by the plate 48. The duct 42 is attached to the bottom of the manifold and to the bustle 18 by the angles 49. The walls and the bottom of the manifold are suitably insulated with the insulation 50.

Figure 6 also shows the well construction which accommodates the tube expansion referred to earlier. Each reaction tube extends through individual holes 51 which are also shown in Figure 5 and which are located in the insu lation of the floor of the furnace. dividual wells 7 are attached to form a substantially gastight cell with the floor. As shown, the well 7 is cup-like in construction with an insulated interior and an access plug 53 on its bottom which may be used to attach a thermocouple to any part of the tube 6. Each we'llis attached to the channels 47 by clip angles 52. Instead of providing an individual well for each tube, a continuous Well or trough for each bank may be used.

In the production of hydrogen from steam and methane where the reactants make a single reactive pass through a t furnace, these problems are involved. The problems are:

(1) All of the tubes should be heated unifrmly.-In order that the reaction may proceed equally in each tube, heat must be supplied uniformly to the tubes and to similar portions of the tubes in each cell.

(2) Provision must be made for the expansion of the. tubes.6ince the usual length of the reaction tubes is about 28 and an expansion of about in the tubes is not uncommon for the operating temperatures, adequate provision must be made for the expansion.

(3) The problem of suspension.An overhead suspended type of tube is desirable for the furnace, and an adequate load-bearing structure must be provided. Moreover, this structure must be protected from the hot products of combustion.

From the foregoing description of a preferred embodiment it will be apparent that all three of these problems are solved by the apparatus of my invention. vThe first problem is solved by the combination of two novel features. The gas-collecting chamber 4 is mounted on the radiant heating chamber 3, the side walls and top 16 of the gas-collecting chamber cooperating to outline the general contours of the tube bank arrangement in the radiant heating chamber. The horizontal partition 14 which constitutes the ceiling for the radiant heating chamber has openings communicating with the gas-collecting chamber. This partition extends beyond the walls 15 of the gascollecting chamber to form the baffles 28 which restrict the openings to areas of vafying cross section so as to equalize the draft in the gas-collecting chamber.

Another feature of my improved furnace is that the burners for each cell are placed in the floor of the furnace adjacent the tubes 6. All of the burners in a cell are supplied with preheated air by a manifold 44 for each cell which constitutes an integral part ofthe floor thereof.

This novel arrangement substantially eliminates the tendency of the hot products of combustion to channel in the radiant heating chamber toward the flue gas outlet or outlets. This is so because the draft in the gas-collecting chamber is the same above .each tube and each bank of tubes. The hot products of combustion therefore pass from the burners which are placed in the floor of the furnace and adjacent the tubes through the radiant heating zone substantially longitudinally and parallel to the entire portion of the tubes disposed therein. Thus all of the tubes and similar units of lengths of the tubes are heated alike and the reaction in each of the tubes proceeds uniformly one with respect to the other. This is one of the principal features and advantages of my improvements.

The suspension means by which the tubes are supported from their upper ends also bears the weight of the novel gas-collecting chamber 4 and the refractory which protects these means from the hot products of combustion. This is accomplished by placing on a foundation 1 substantially vertical load-bearing walls 2 Below each hole ingas-collecting chamber.

6 which enclose the radiant heating chamber 3 and the gas-collecting chamber 4. Transverse beams 9 extending across the central portion of the furnace are mounted at the top of the walls 2 and are supported by them. Tension members 10 are suspended from the beams 9 and extend downwardly into the central portion of the furnace. An upper and a lower set of transverse beams 11 and 12 are attached at their inner ends to the tension members 10 and at their outer ends to the vertical walls 2. The tension members and the transverse beams cooperate with the walls to outline the surmounted chamber 4 and from them are hung the tubes 6, the inlet and outlet manifolds 19-and 22, the ceiling of the radiant heating chamber 14 and the walls 15 and top 16 of the The suspension of these ele ments is carried out in such a way that the suspending means are protected from the hot products of combustion in the furnace.

One advantage of the suspension feature of the invention is that the tube supports do not shield any of the so-called working part of the tubes from the heat. Another advantage of the suspension feature is that the upper portion of the tubes and the means by which they are suspended from their upper portion are placed adjacent that part of the furnace where the hot gases are at their lowest temperature. This arrangement also allows the furnace to be operated up to those temperatures where the working portion of the metal-alloy tubes becomes soft. 7

Although in the preferred form my furnace is circular in shape with twenty reaction tubes disposed in cruciform arrangement, there are a number of alternate forms within the scope of my invention. Thus, for example, any number and size of tubes supported from their upper or lower portions may be arranged in any number of banks which radiate symmetrically or unsymmetrically from the center of the furnace. Likewise the gas-collecting chamber may be made to function as a convectionheating chamber and where fluid heating tubes are used, whether or not the gas-collecting chamber functions as a convection heating chamber, they may also have extensions or fins on either or both sides of the outer tube and on the outside and inside of the inner tube.

Although it is preferred to have a single row of tubes in any bank and to carry out the same reaction at the same rate in all the cells formed by the banks of tubes, a plurality of rows of tubes may be used in a bank and the same reaction can be carried out at various temperatures in the various cells of the furnace and even different reactions can be carried out in the various cells if so desired.

Instead of the single stack outlet disclosed above, two or more stack outlets may be used as well as a stack outlet for each section of the surmounted chamber and this may be particularly desirable When this chamber is used primarily as a convection heating chamber. Wherever a stack outlet is used the baffie construction should conform to that of section 26 in Figure 2 in that pro ceeding from the center of the furnace to the walls the baffles should extend progressively farther into the openings in such a way as to equalize the draft within a section and one section with respect to another.

I claim:

1. A fluid heating furnace comprising in combination a lower radiant heating chamber formed 'by a floor and substantially vertical side walls surmounted by anupper convection chamber having a top and side walls and being smaller in cross sectional area than said lower chamber, a stack outlet on a side wall of said upper chamber, a horizontal partition constituting a ceiling for said lower chamber, said partition extending inwardly from the side walls of said uppercha mber for varying distances so as to form elongated openings of varying cross section communicating with said upper chamber the size of said openings varying in proportion relative to their respective distances from the stack outlet to equalize the draft, a number of vertical tubes extending from the floor of the lower chamber through said openings to the top of the upper chamber and fuel burners in the floor of said lower chamber adjacent said tubes. 2. A fluid heating furnace comprising in combination a lower radiant heating chamber formed by a floor and substantially vertical side walls surmounted by an upper convection chamber having a top and side walls, a horizontal partition constituting a ceiling for said lower chamber and having a plurality of elongated openings therein extending radially of the vertical axis of the heating chamber and communicating with said upper chamber, fuel burners in the floor of said lower chamber and a stack outlet in a lateral peripheral portion of said upper chamber to carry off the hot combustion gases from said burners, a load bearing framework above the top of said upper chamber and insulated from the hot gases therein, a number of vertical tubes suspended from said framework and extending downwardly through the top of said upper chamber and through the openings in said partition to the floor of said lower chamber, one of said openings being adjacent said stack outlet and increasing in cross section in the direction from said outlet toward the vertical axis of the heating chamber and the other openings decreasing in cross section in the direction from the side walls toward said vertical axis whereby the path of said hot cornbustive gases through said furnace is longitudinal of the tubes in said lower chamber and transverse thereof in said upper chamber.

3. A fiuid heating furnace comprising in combination a lower radiant heating chamber formed by a floor and substantially vertical side walls surmounted by an upper chamber having a top and side walls, a. horizontal partition constituting a ceiling for said radiant heating chamber having cruciform openings communicating with said upper chamber, banks of vertical tubes in cruciform arrangement disposed in said openings and extending from the floor of said lower chamber through the top of said upper chamber and dividing both chambers into a plurality of cells, said upper chamber having the general contour of said bank arrangement, a loadbearing framework above said upper chamber and insulated therefrom to support said tubes, a stack outlet on a lateral peripheral portion of said upper chamber and communicating with one of the cells therein, burners in the floor of said lower chamber and adjacent the tubes, a manifold forming an integral part of said floor in each cell and in which said burners are placed to supply preheated air thereto, one of said openings being adjacent said stack outlet and increasing in cross section in the direction from said outlet toward the vertical axis of the heating chamber and the other openings decreasing in cross section in the direction from the side walls toward said vertical axis to equalize the draft in said cells of said upper chamber whereby the path of the hot combustion gases from the burners in each cell is longitudinal of the tubes in said lower chamber and transverse thereof in said upper chamber.

4. A fluid heating furnace comprising in combination a foundation, substantially vertical load-bearing walls on said foundation enclosing a lower radiant heating chamber and an upper chamber surmounted thereon, transverse trusses mounted at the top of said walls and supported thereby and extending transversely across the top portion of said furnace, tension members suspended from said trusses and extending downwardly, an upper set of transverse beams attached at their inner ends to said tension members and at their outer ends to said vertical walls, said set of transverse beams being located between the top of said furnace and the lower extremities of said tension members, a lower set of transverse beams suspended under the upper set, said tension members and transverse beams cooperating with said walls to outline said upper chamber, a plurality of vertical heating tubes extending downwardly through both said upper and lower chambers, means to suspend said tubes from said upper transverse beams and means to suspend heat refractory material from both said sets of transverse beams to form a ceiling for said lower chamber and ceiling and walls for said upper chamber.

5. A cylindrical fluid heating furnace comprising in combination a foundation, substantially vertical, cylindrical load-bearing walls on said foundation enclosing a lower radiant heating chamber and an upper chamber surmounted thereon, radially arranged banks of vertical tubes extending downwardly through both said chambers and dividing both chambers into a plurality of heating cells, transverse trusses mounted at the top of said walls and supported thereby and extending transversely across the top portion of said furnace, tension members suspended from said trusses, an upper set of transverse beams attached at their inner ends to said tension mem bers, and at their outer ends to said vertical walls, said upper set of beams being located between the top of said furnace and the lower extremities of said tension members, a lower set of transverse beams suspended under the upper set, said tension members and transverse beams cooperating with said walls to outline the general contour of said tube bank arrangement in said upper chamber, means to support said tubes from said upper transverse beams and means to suspend refractory material from both sets of transverse beams to form a ceiling for said lower chamber and ceiling and walls for said upper chamber.

6. A fluid heating furnace comprising in combination a heating chamber and a gas-collecting chamber, said heating chamber being formed by a floor and cylindrical side walls and having a horizontal partition constituting a ceiling, said partition having a common opening in the center thereof and a plurality of elongated openings each connected to the common opening and radiating therefrom toward the side walls, said elongated openings varying in cross sectional area so that the draft is equalized, said gas-collecting chamber being positioned above the heating chamber and having a top and side walls, said side walls extending upwardly from the elongated openings in the partition to the top of said gas collecting chamber whereby the latter is in the form of a corresponding plurality of radiating sections, a plurality of tubes extending from the floor of the heating chamber through the elongated openings into the gas-collecting chamber, fuel burners in the floor of the heating chamber for heating the tubes and a stack outlet in the gascollecting chamber for removing the burner gases.

7. A fluid heating furnace comprising in combination a heating chamber and a gas-collecting chamber, said heating chamber having a floor, side walls and a partition member constituting a ceiling, said partition member having a common opening in the center thereof connected to a plurality of elongated openings radiating toward the side walls, said gas-collecting chamber having walls coinciding with the edges of the elongated openings and extending upwardly from the partition member so as to form the gas-collecting chamber into a plurality of sections, a plurality of tubes extending into both chambers and passing through the elongated openings,

fuel burners in the floor of the heating chamber for heating the tubes, a stack outlet at the outer end of one of the sections of the gas-collecting chamber for removing the burner gases and a plurality of bafiles in the form of a continuation of the partition member protruding into all of the openings so that the cross sectional area of the opening into each section is reduced progressively from the side walls of the heating chamber toward the center thereof except the opening leading to the section containing the stack outlet in which the cross-sectional area increases progressively from the side walls of the heating chamber toward the center, wheieby the draft is equalized in each section of the gas-collecting chamber and also in each section with respect to the other sections. 5

8. A fluid heating furnace comprising in combination a lower radiant heating chamber formed by vertical side walls and a floor having fuel burners therein, an upper convection chamber having a top and side walls and being smaller in cross sectional area than said lower chamber and surmounted thereon, a stack outlet in 'a lateral peripheral portion of said upper chamber, a horizontal partition extending inwardly from said side walls over the major area of said lower chamber and constituting a ceiling therefor, a plurality of elongated openings in said partition extending from the central portion of said furnace toward the side walls thereof, one such opening being adjacent said stack outlet and increasing in cross section in the direction from said outlet toward the central part of the furnace, the other openings decreasing in cross section in the direction from the side walls toward said central part of the furnace to equalize the draft in said upper section, anda number of vertical tubes extending through said openings from the floor of said lower chamber to the top of said upper chamber, whereby hot products of combustion from said burners pass longitudinally of said tubes in said lower chamber and transversely thereof in said upper chamber.

References Cited in the file'of this patent UNITED STATES PATENTS 1,881,275 Hufi Oct. 4, 1932 2,105,500 Parsons Jan. 18, 1938 2,151,386 De Florez Nov. 21, 1939 2,211,903 McCarthy Aug. 20, 1940 2,454,943 Reed Nov. 30, 1948 2,514,279 Gleber July 4, 1950 

